A/N: BEWARNED! SPOILERS FOR AGE OF ULTRON BE AHEAD! I don't mind Bruce/Natasha and in fact I find it a bit refreshing, but I wish there was a better build up. More of a reason; I mean, after the movie I see potential, but it's the premovie stuff that they don't show that I want to know about. For me, this is the beginning. It's set after The Avengers, but before CAWS, as Natasha is still here,

Sing Me a Lullaby

Natasha descended the steps down to the lab where Bruce was deep in his work. "Bruce," she said softly.

"Hmm," he looked up and smiled when he saw Natasha.

"I have an idea."

He pulled his glasses off and rolled away from the lab table. "For what."

"For when, you know, the other guy comes out."

"Natasha, it's a nice offer, but I can't let you-"

"Banner, we both know that if you can't contain the Hulk civilians can be harmed."

He sighed. "I have everything under control, Romanoff. I do yoga. I'm relaxed."

"That's not what I mean. I mean afterwards, when we've already won and we need you back. We need a plan of action."

"Natasha."

She crossed her arms. "I'm sorry, but their Fury's orders."

Bruce leaned back in his chair and crossed his arms. "But why are you the one doing this."

She shrugged her shoulders. "I almost had you in the helicarrier; you almost came back. I want to try something and I think it might work."

Bruce rolled back over to his lab table. "Thanks, but no thanks. I'm not hulking out here and putting potential citizens in harm's way."

She shook her head. "I'm not talking about bringing out the other guy. At least not yet. I want to practice with you. If you recognize it as Banner I think it will work to bring you out of the big guy."

Bruce sighed and pushed his chair back out and gestured to the one beside him. "Five minutes. And then we don't talk about it for a while."

Natasha nodded and sat down. "If that's what you want Banner." She evened her breathing and looked Banner in the eye, staring into his soul. "To start, we need a key phrase. Something that will prepare you for what will come next. Reminding you of what's happening."

He blinked. "Do you have anything in mind?"

"The sun is setting soon."

Bruce rubbed the back of his neck. "I don't know Romanoff-"

"That's not all of it. It's just the trigger."

"Then what's the other part?"

She held up her hand facing him. "Now hold yours up to mine."

He looked hesitantly at her before letting his palm just ghost over hers.

She breathed in and slowly pushed her hand forward, touching his hand. She lifted it back before carefully running her hand down his forearm; her fingers gently caressing his arm. She felt Bruce tense up under fingers. "Relax, Banner." He let go of his held breath as her fingers trailed back over his hand, just barely latching on as her fingertips pulled up. "What do you think? Will it work?"

Bruce ran his hand over his face. "I don't know. It might, it might not. The only way to test it is if I let the other guy have control and I really don't want to do that."

She sighed. "Then let's try it again." She looked him in the eyes. "Hey, the sun is setting soon." She continued to stare into his eyes as she went through the motions, never losing contact. As her fingers danced down his arm she faintly felt his pulse elevate.

Bruce started to even his breathing to keep his cool. When Natasha finished she didn't break eye contact until Bruce cleared his throat. "Um, uh, I think that's enough for one day, don't you?"

She nodded. "Of course we can work on this some other time." She left the lab and walked up the stairs. She entered the elevator to go back to the main floor and met Steve inside. "How did it go? Did it work?"

Natasha sighed. "I don't know. I really won't know until the big guy's here."

Steve patted her shoulder. "You're taking baby steps and that's fine. It won't work if Bruce is resisting you."

"You're right, but...JARVIS?"

Yes, Miss Romanoff?

"Take me back down to the lab and whatever you do don't let the others interfere, especially Tony."

As you wish

The elevator began to descend.

"Nat, what are you doing," asked Steve cautiously.

She pulled a gun from her holster and checked the clip. "I'm not taking baby steps, Rogers." The elevator doors opened and she stepped out.

"Romanoff, come back here!"

She switched the safety off. "JARVIS, please detain Rogers in the elevator until further notice."

Certainly, Miss Romanoff

The elevator doors closed leaving Steve inside banging on the door.

She flipped her hair out of the way and started to sneak forward.

"Tony," she heard Bruce shout, "is that you?"

She aimed and fired, letting the bullet just barely graze Bruce's arm. His hand went up to the wound in shock. She watched as his eyes flashed green and she heard muscle, skin and bones crunch as they grew in size. She was mesmerized as Bruce turned into the massive Hulk. With a scream he began to throw objects out of his way as he rampaged across the lab, looking for the shooter.

Natasha put her gun away and slowly stepped out from her hiding spot, hands up. "Hey!"

Hulk looked over and frowned at her.

She took a deep breath. "The sun's setting soon."

Hulk growled and slapped her out of the way and into the glass wall, causing it to shatter.

"Natasha," shouted Steve from inside the elevator. "JARVIS, let me out!"

She sat up and pointed at the elevator. "Don't you dare! JARVIS, Keep him in there." She flipped forward and landed in front of the Hulk. He tried to punch her, but she rolled and dodged. He reached out and grabbed her by the leg; roughly throwing her up in the air.

She grabbed hold to an exposed pipe before dropping back down when his back was turned. He heard the soft thud she made as she connected with the floor and he reached out and grabbed her by the waist. He pulled her relatively closed to his face and screamed. Her breathing was labored. "The sun is setting soon."

Hulk frowned at her again and started to throw her down, but she stuck her hand out. Hulk cocked his head to the side and slowly raised his hand up to hers.

Natasha blinked rapidly as she saw her small pale hand against his gigantic green one. She slowed her breathing, never breaking eye contact, as she pulled her arm away and began to trace her fingers across his veins.

Hulk watched her delicate fingers as they moved down his arm, briefly stopping at his wrist. She continued until she held on by only her fingertips, letting them linger before slowly slipping them away.

The Hulk dropped her to the floor and began to stagger backward, confused. Natasha watched as he fell to the lab floor and he began to shrink back into Bruce. She sat up from the rubble and walked over to him. He sat up with dazed eyes looking around. "Natasha." He looked at her cuts and scrapes, the blood in her hair.

"Natasha, are you all right? Did I hurt you?"

"I'm fine Bruce," she said. "JARVIS, you can let Rogers go."

Of course, Miss Romanoff

The elevator doors opened and Steve came out angry. "Natasha, what the hell was that for! You put the team and the city in danger!"

Bruce looked at her and his eyebrows scrunched together. "Natasha, what's Steve talking about?"

She shot an evil glare towards Steve. "I didn't want to wait until it needed to work. I had to try."

Bruce raised his hand to the burned and raw skin on his arm where the bullet grazed him. "You," he whispered.

Steve stepped closer in between the two. "Let's talk about this later. After you both have had time to calm down."

Natasha pulled her gun out and shot the wall behind Steve, the bully's barely missing his hair. "Rogers, I don't need you trying to be Captain right now. I can handle this."

He crossed his arms. "Romanoff, you ignored a direct order from me earlier and you could have put others in harm's way without any regard for them."

Natasha got up into his face and poked him in the chest. "Listen here, Rogers-"

"Both of you stop," yelled Bruce.

Natasha looked over at the scientist and saw a faint shade of green gleam in his eyes; his fingers began to twitch and a vein popped in his neck. She tensed up. "Steve, can you trust me?"

He looked over at Bruce and then back at Natasha. "Promise not to do anything stupid?"

She edged closer to Bruce who was bent over on the floor and turning a faint shade of green. "Nope."
He nodded. "Okay then."

"Stand guard by the lab door make sure he doesn't get out," said Natasha as she sat down in front of him. She leaned down until she was face to face with him.

"Natasha-no. Get. Back," choked out Bruce. She could see that he was visibly trying to hold himself back.

"Hey," she grabbed his chin and forced him to look at her. She could see the concern and despair in his eyes. "The sun is setting soon."

He grabbed her arm and tried to gurgle out choked back words. She ran her hand down his arm until she reached his hand and she laced her fingers in his. His labored breathing became calmer and the green began to recede from his face. "Na-tash-a."

"Yeah, Bruce, it's me."

He fell against her shoulder and she let go of the breath she was holding. He sat back and looked at her with weary eyes. "It worked."

"Yeah," she whispered, "it did."

"Promise me you'll never do that again."

She looked around at the shattered glass, ruined technology and the haggard man in front of her. "Promise."

Steve walked back into the lab. "Natasha-"

"I don't want to hear it Steve."

"No, good job."

"Thanks."

Steve looked at the two and then cleared his throat. "I'll, uh, go see if Stark noticed anything." He re-entered the elevator and left the two in the rubble.

Natasha looked at her surroundings. "Stark is going to be so pissed when he finds out."

Bruce shrugged. "Well, I guess I've always been a liability."

"Don't say that about yourself."

"It's okay; I've learned to accept it." He stood up and brushed dust off of himself. "I-I've got go, you know," he gestured to his tattered clothes, "clean up."

Natasha nodded. "Of course." She watched as he walked away, knowing that something changed in their relationship.